Near field communications (NFC) devices are becoming increasingly popular, in sectors such as banking, as they permit rapid exchange of data over a short range (less than 10 cm), which can be used to facilitate making small value payments, for example.
In recent times, interest in incorporating active NFC devices such as NFC readers in small portable devices such as mobile telephones has grown.
At present, in order to perform an NFC transaction, an active NFC device such as an NFC reader must generate a magnetic field with which DC power can be delivered to a receiving NFC device, which may be a passive NFC device such as a tag. The current required to generate such a magnetic field around an antenna of the active NFC device may be as high as 100-200 mA, and this type of operation, which is known as Reader Emulation Mode (REM), may need to be continued for an extended period of time in a search mode in which the active NFC device tries to identify a compatible NFC device with which to perform a data transaction.
When REM is used by an active NFC device such as a reader to search for compatible NFC devices, a signal modulated with data is transmitted by the reader, which awaits a reply. When a reply is received, a data transaction can take place between the active reader and the replying device. It will be appreciated that this process of searching for compatible devices can occupy a high proportion of the operating time of the NFC device and thus consumes a considerable amount of power, which is undesirable in portable devices such as mobile telephones which have limited battery resources.